Fabrication and target applications of hydrophilic-hydrophobic composite wettability surfaces based on surface wettability gradient and Laplace pressure gradient regulation

Hydrophilic-hydrophobic composite wettability surfaces have shown great potential in various fields such as water harvesting, oil-water separation, microfluidic devices, the controllable adhesion of proteins and cells, microchips, and microreactors. In particular, the surface energy gradients and Laplace pressure gradients resulting from differences in surface wettability and hydrophilic-hydrophobic patterned structures make them more efficient than traditional single wettability surfaces. In this review, the fabrication methods of composite wettability surfaces are summarized, and the theories behind the regulation of surface energy gradients and Laplace pressure gradients are discussed. Based on the surface energy gradient and the Laplace pressure gradient, we also evaluated the functional characteristics and target applications of different types of composite wettability surfaces and proposed ideas to optimize these functional properties. Finally, the limitations of the current regulation theories are briefly mentioned with expectation that more research will be done to improve these theories and enhance the functional properties of composite wettability surfaces.